Listeners are able to localize sources of sound primarily because of differences in the sounds arriving at the two ears. When sounds are heard with headphones or out of doors; 'these interaural differences | are systematic and reliable. But in a room environment, reflections from the room surfaces distort the sound field leading to localization difficulties and requiring listeners to adopt a variety of unconscious strategies for dealing with the situation. The effects can be especially pronounced for hearing impaired individuals. Research proposed in this application has the long-term goal of predicting the confusions and revised strategies experienced by listeners based on improved understanding of the human binaural system and of the acoustics of rooms. Steps toward that goal focus mainly on the human listener and ask the following questions: What is the effect of a room on a listener's ability to distinguish sounds coming from the left or right, as compared with the ability to identify sound sources? What aspects of a sound waveform best describe the perception of binaurally different signals including the detection advantages of binaural differences? Can the results of experiments using idealized sounds presented by headphones be transferred to predict localization abilities in the real world? It is possible to find a neurophysiologically-based model that explains localization deficiencies caused by reflected sounds, especially the effects of frequency range? How do listeners use information in the onsets of sounds, arriving before the reflected sound field builds up? Do timing parameters, and left-right asymmetries observed in idealized conditions really affect the use of onset information in ordinary environments? These questions are addressed by a combination of binaural recordings and measurements in rooms, listening experiments in rooms and with headphones, and virtual reality simulation in a reflection-free environment. The virtual reality techniques are notable because they promise unprecedented control over the high-frequency information that listeners use to distinguish between sounds coming from the front or the back. The new research is particularly relevant to the use of auditory prostheses in ordinary room environments. [unreadable] [unreadable]